Project 1: Amyloid Beta SUMMARY/ABSTRACT Alzheimer's disease (AD) is characterized by the accumulation of amyloid-? (A?) and neurofibrillary tangles composed of the tau protein in the brain. More than 200 mutations have been identified in amyloid-? precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) that cause autosomal dominant forms of AD (ADAD). PSEN1 and PSEN2 form the catalytic domain of the ?-secretase enzyme, which cleaves APP to generate many A? proteoforms which can be modified into variants including posttranslational modifications, truncations and sequence variations. Changes in the relative ratios of A?42/40 isoforms have been used to predict pathogenicity of ADAD variants. However, we know less about the contribution of other A? proteoforms to AD pathogenesis and the utility of the A? proteoform signature as a biomarker of mutation status and/or disease course. For example, what are the A? pathogenic cause(s) of ADAD? Several A? proteoforms support a causal role for AD, including A?42, A?43, A?37, A?39 and modifications including pyroglutamate, oxidation, isomerization, and N- and C-terminal truncation. The objective of this study is to define the effects of ADAD mutations and amyloidosis on A? proteoform and disease pathogenesis. To meet this objective, we will define mutation and gene-specific effects on A? proteoform signatures using novel mass spectrometry approaches in human plasma, CSF, stem cell derived neurons, and brain tissue. We will then determine how A? proteoform signatures relate to histologic amyloid plaque structure in human brains. We hypothesize that ADAD mutations produce a common pathogenic A? proteoform signature. The rationale for this proposal is that defining the effects of ADAD mutations and amyloidosis on A? proteoforms will be critical to define the common pathogenic A? signatures which cause AD. This target validation will guide clinical studies, therapeutic strategies and classify future novel ADAD mutations. This work will be performed in collaboration with the Genetics, Biomarker, Clinical, Neuropathology, Imaging, and Biostatistics Cores.